1. Field of the Invention
The present invention relates to a method of fabricating an optical branching and coupling, device which is accomplished by bringing coating partly stripped portions of a plurality of coated optical fibers into close contact with each other in a direction perpendicular to the optical axis, and unifying the coating stripped portions by melting them upon heating.
2. Prior Art
Optical branching and coupling devices may be classified by their components and functions into three groups: optical component utilization type, optical fiber utilization type and optical waveguide type. Of these, the optical fiber utilization type has advantages including that the number of components required is small because they can do away with the optical components such as lenses and their fabrication is easy, among others.
The conventional method of fabricating the optical fiber branching and coupling device of such an optical fiber utilization type will now be described. The methods of fabricating the optical branching and coupling device using an optical fiber can be roughly divided into a grinding method, etching method and melt-fusion method. The grinding method shaves off the clad part of the optical fiber and the core parts of the optical fibers are then allowed to be close with each other. The etching method immerses the clad parts of the optical fibers in a highly acidic or alkaline solution so as to be etched, and the clad parts thus etched are twisted to be brought close with each other.
Further, as to the melt-fusion method, there are two methods depending upon the conditions in arrangement of two optical fibers. The first method is one in which the coating of each of the two coated optical fibers is partly removed, and the two fibers thus coating-removed are twisted and melted by heating in such a manner that they are unified (disclosed in Stable Low-Loss Single Mode Couplers, Electronic Letters, Mar. 15, 1984, Vol. 20, No. 6, pp. 230-232. The second method is a method partly removes the coating of each of two optical fibers, arranges them in parallel, and melts them by a heating process so as to unify the melted portions thereof (disclosed in Japanese Patent Publication Gazette, No. 60-501427).
However, it is difficult to finish the fiber with an accuracy of the order of a micron by the grinding method and the etching method, so that their practicality does not amount too much at present.
Further, the conventional melt fusion method has been applied to melting and fusing two single-core coated optical fibers, and it has been difficult to be applied to branching and coupling a large number of optical fibers (for example, multi-core coated optical fibers) at one time.
In that case, a protective material for protecting the optical coupling portion is required for every pair of optical fibers so that a high density mounting is difficult.